Hitherto, minute patterning by lithography using photoresist compositions has been performed in processes of s manufacturing semiconductor devices, such as ICs and LSI. Recent growing need for larger packing densities of integrated circuits has come to entail super minute patterning in the submicron or quatermicron region. In response to such a requirement, the light sources used in photolithography are showing a tendency to have shorter wavelengths. Actually, the light for exposure use have been changed from g-ray to i-ray, and further to KrF excimer laser beam. And nowadays the development of lithographic processes using not only excimer laser beams but also electron beams and X-rays is proceeding.
Electron-beam lithography is placed as a next-generation patterning technology or a generation-after-next patterning technology, and it is desired to develop positive resist highly sensitive to electron beams and capable of forming highly resolved patterns. Increasing sensitivity in particular is a very important problem in pursuing reduction of wafer processing time. As to the electron beam resist, however, pursuit of increased sensitivity results in not only lowering of resolution but also deterioration of line edge roughness. Therefore, it is strongly desired to develop resist compositions satisfying such quality requirements at the same time. The term “line edge roughness” as used herein means rough appearance the pattern-substrate interface edge has when resist patterns are viewed from right above, wherein the roughness of the pattern-substrate interface edge arises from irregular fluctuation in a direction perpendicular to the line direction resulting from resist properties. Transfer of this roughness occurs in the etching process using the resist as a mask and gives rise to deterioration in electric properties and decrease in yield rate. Therefore, improvement of line edge roughness is a very important problem, especially in the superfine region of 0.25 μm or below. High sensitivity bears a trade-off relation to high resolution, pattern profiles of good quality and satisfactory line edge roughness, and so how to satisfy these properties at the same time is a very important problem.
And also in the lithography using excimer laser beams with short wavelengths, such as KrF excimer laser, as exposure source, formation of fine patterns in the region of 0.20 μm or below is targeted for. As in the case of electron beam lithography, there is a trade-off relation between properties including sensitivity, resolution, pattern-profile quality and line edge roughness, and so it is intensely desired to develop resist compositions satisfying those quality requirements at the same time.
As resist suitable for lithographic processes using electron beams and KrF excimer laser, acid catalyst-utilized chemical amplification resist has been mainly used from a sensitivity-oriented point of view. With respect to the positive resist, chemical amplification resist compositions containing as main components a phenolic polymer having a property of being insoluble or hardly soluble in an aqueous alkali solution but becoming soluble in an aqueous alkali solution by undergoing the action of an acid (hereinafter referred to as a phenolic acid-decomposable resin) and an acid generator have been used effectively.
Such positive resist has undergone continual performance improvements made with attention to its constituent polymer and acid generator. For instance, JP-A-2-19847 discloses the resist composition containing the poly(p-hydroxystyrene) whose phenolic hydroxyl groups are totally or partly protected by tetrahydropyranyl groups, and JP-A-4-219757 discloses the resist composition containing the poly(p-hydroxystyrene) in which 20 to 70% of the phenolic hydroxyl groups are replaced by acetal groups.
As to improvements from the standpoint of an acid generator, JP-A-2000-292917 discloses the combination of an acid-decomposable polymer containing carboxyl groups protected by acid-decomposable groups, an acid generator of a specified phenacyl structure and a triphenylsulfonium salt, JP-A-2001-294570 discloses application of the phenacylsulfonium salt of a specified structure to positive resist, and JP-A-4-211258 discloses the combination of a specified acid-decomposable phenolic resin and a specified phenacylsulfonium salt.
However, it is the present condition that any of the aforementioned combinations and arts cannot satisfy all of high sensitivity, high resolution, pattern profile of good quality and satisfactory line edge roughness at the same time.